ROBERT CHAMBERS 43 



starfish egg. It is also of interest to note that the fertilizability of 

 the egg fragments is directly connected with the extent of the mixing 

 of the nuclear sap with the cytoplasm in the maturing egg. A non- 

 nucleated fragment, taken from an egg in the early stages of the 

 dissolution of the germinal vesicle, will admit sperm which will 

 undergo several nuclear divisions with, at most, an abortive attempt 

 on the part of the fragment to cleave. When the sap of the germinal 

 vesicle has completely mixed with the cytoplasm, any fragment 

 larger than a certain size limit is capable of being fertilized and 

 undergoing cleavage. 



It is well known that immature eggs can be kept in sea water at 

 room temperature for 24 hours or more without disintegrating and 

 that unfertilized mature eggs go to pieces under the same conditions 

 within a much shorter time.^ The writer has found that nucleated 

 fragments of the two kinds of eggs behave similarly, while non-nucleated 

 fragments act quite differently indicating that the substance which 

 prevents the disintegration is distributed differently in the two eggs. 

 Non-nucleated fragments of immature eggs last for about 4 hours 

 only. Similar fragments of mature eggs last from 8 to 10 hours, or 

 about as long as the mature, nucleated fragments. The substance 

 which prevents the destruction of the egg is apparently in the nuclear 

 sap which, in the immature egg, is confined within the large nucleus 

 or germinal vesicle, while in the mature egg this sap has escaped 

 from the nucleus and spread throughout the entire egg. 



The following experiments indicate that the part of the starfish 

 egg which is capable of development is chiefly confined to the cortex 

 of the egg. It was long ago shown by Driesch,' Loeb* and others 

 that starfish and sea-urchin eggs are highly fluid in that fragments 

 quickly round up into spheres. That the cortex of the mature un- 

 fertilized eggs is firmer in consistency than their interior has been 



^Loeb, J., and Lewis, W. H., On the prolongation of the life of the unfertilized 

 eggs of the sea-urchins by potassium cyanide, Am. J. Physiol., 1902, vi, 305. 

 Loeb, J., Maturation, natural death and the prolongation of the Ufe of the unfer- 

 tilized starfish eggs (Asterias forbesii) and their significance for the theory of 

 fertilization, Biol. Bull, 1902, iii, 295. 



^ Driesch, H., Entwicklungsmechanische Studien. Der VVerth der beiden 

 ersten FurchungszeUen der Echinodermcntwicklung, Z. iviss. Zool., 1891, liii, 60. 



^Loeb, J., Ucbcr die Grcnzen der Thcilbarkcit der Eisubstanz, Arch. Physiol., 

 1895, lix, 379. 



